Free machining carbon steel



Patented July 30, 19 35 4 J s PATENT OFFICE 2,009,714 FREE micnmmo cannon 'srerzr.

Frank R. Palmer, Reading, Pa, assignor to The Carpenter Steel Company, Reading, Pa., a corporation of New Jersey i 'No Drawing. Original application January 14,

1932, Serial No. 586,697. Divided and this ap- 'plication March 9, 1934, Serial No. 714,828

9 Claims. (Cl. 75-1) a This inventionrelates generallytoferrous prod- 98% iron fall within the scope of my- "straight ucts adapted for use in the manufacture of macarbon steel group. f chined articles having relatively free machining S. A. E. specifications provide for certain free qua ity impartedthereto by a seleniumtellurium machining types, as for example X1315, 1112 and content, as fully set forth in my copending ap- 1120 which contain deliberately added sulphur 5 pllcation Seig;flo..,586,697 filed January 14, 1932; with or without deliberately added phosphorus UNITED 1 STATE the presenfhhprovement forming a division of for purposes of free machining. Such high sultheaforesaid application, and relating particuphur free machining steels have lon b n k w larly to the so-called straight carbon class debut their commercial application is materially l0 scribed therein. limited by the notoriously poor quality of the prod- 10 In said applicationIpointed out that the ferrous not. It is generally conceded that sulphur comalloys referredto might conveniently be divided ines with some metal in the composition to form into four general classes designated asstraight a metal-sulphide (usually manganese sulphide) carbon steels, '-structural alloy steels, tool having Hon-metallic lag-l ke properties. These steels and special alloy steels as fully descr b d inclusions are hardly soluble in the ferrous 15 in said application. The invention described m trix.-h vine glo ular f rm in the a t ingot herein applies to the first of the before mentioned a ing d wn O t 111150 0 8 stringers in r l d groups-namely, straight carbon steels,*whieh 0r drawn products. In thisformthe inclusions is defined for my purpose as comprising all ferrous greatly d p e t e t n e s ductility o t e 1 alloys containing more than 98% iron. .The metal and sodecrease the general quality of the my balance may consist of carbon, manganes a d steel to a point which interferes with its comsi on with a small quantity of other alloying mercial application,-notwithstanding the deelements and a minimum of undesirable impurisirability of f eem h s p p t ties,.totallingnot more than 2%. Providing th I have determined that free machining proppercentage of iron does not fall below 98%, erties may :be' introduced into these -s traight 5 ferrous alloysinthisstraight-carbon group may carbon steels'by the addition of irom 03% to contain smallpercentagesof so-called alloying 1.50% of the metalloidsselenium andtellurium, elements deliberately added but present in h used individually'or jointly. Selenium and tel; small amounts as ,to hardly warrant theinbeing l'urium appear also to combine with a metalto calledalloy steels; such elements as vanadi m, form metal-selenldes 'or metal-tellurideslhavingi o tungsten, copper, molybdenum, chromium,'nick 1, non-metallic or slag-like properties.- However, sulphur, phosphorus, etc., being typical of tie he selenides'or tellurides appear to :belargely additions referred to. so-c l ed "ingot r n", soluble in the, ferrous matrix because in any containingaminimum f n n-f rr us l m ts, event they are found in much smaller quanti- .35 also comprehended by the straight cflbon" ties'under the microscope thanwould be found group. p with an equal percentage of sulphur in the com-.

Inthe specifications of the American-Society position. The smaller quantity of slag-like in- Automotive Engineers, published in t s a; clusions in the selenium or tellurium steels makes handbook dated 1930 to which reference is made, them much cleaner d gf li cq th t i carbon steels are com rem mercial applications; fur ermore e trans- 40 the s. A. E. 1000 series. obviously eri'ol l s og verse ductility is higher than, with can be compounded outside 3 such equal percentages of sulphur due to the'fact exam thatcontinuity of the ferrous matrix is not ins'A'E'specmcafionsasmr plecppper bear terrupted to such a degree by slag-like stringers.

35 mg steels mpw'mmybdePum steels used for My experiments further indicate that selenium corrosionresxstancemommemlm pure ingot iron and tellurium are somewhat more potent than tool steels containing more than 1.10% carbon,

sulphur. For this reason when usedin the same vanadium steels containing about 30% to quantities as sulphur, the resulting machining 30% Vanadium etc-i an which my Purpose properties, are superior; or equal machining fall within the "strai ht carbon" oup providing properties may be procured in my steel with 50.

the nc is more an 98%. Among t smaller percen ges of selenium or ,tellurium S. A. E. steels are found such compositions as T than would be required in a sulphur steel; which x1315 containing low carbon, 1.25% to' 3 .55% facts contribute further to the cleanness and m nganese,.105% phosphorusran'd'.080'% to.130% commercial applicability of my improved'.al1oys. 191mg, hi since they e m moi-e My experiments with tellurium confirm :the 55 published medical statements regarding the poisonous nature of this element. Tellurium when added to a bath of molten steel gives off copious white fumes which are very disagreeable and dangerous to the workmen. Selenium also gives oif white fumes, but these appear to be relatively unobjectionable as no poison effects have been observed by workmen even after several years experience with the use of selenium in the melting shop. I regard tellurium as particularly dangerous and objectionable in these straight carbon steels because such steels are usually made in open hearth furnaces and the metalloid additions would naturally be madein the ladle where there is little opportunity for the use of hoods or other safety devices for carrying off the tellurium fumes. For this reason I do not-regard tellurium as practically avail: able for my purpose although I have done enough work with it to determine that its presence in the steel achieves the purpose of my invention as was demonstrated for example by machining tests made on straight carbo'n steels of the following analysis:

' 0. Mn Si P 8 Te In the case of selenium in which my work has been more extensive due to its non-poisonous nature I find that the machinability of straight carbon steels shows slight but noticeable improvement with percentages as low as .05% selenium and that the machinability increases progressively as the'selenium content is increased up to about 25%. Further additions of selenium up to 1.50% give furtherprogressive improve- .ment but at a slower rate so that I contemplate Quite small percentages of selenium can also be used to supplement small percentages of sulphur, the effect on machinability apparently being cumulative. For example many specifications limit sulphurto less than 04% or .05%, but when supplemented by as little as ;03% selenium, the total percentage of sulphur-selenium metalloid may be as much as .07 or .08 which is suificient to react favorably on themachining properties of the alloy. Thus my invention is commerically usable with selenium even as low as .03%.

The use of phosphorus in straight carbon screw stock such as S. A; E. 1112 is recognized by the art. Phosphorus has an embrittling effect which .is sometimes desirable 'in producing free machining properties, 'i

In the use of my invention on steels that are soft, tough or stringy to machine, there are apparent advantages .to employing phosphorus in conjunction with selenium to further improve "the machinability. The embrittling eflfect of phosphorus is progressive and can be used up to in extreme cases, however the more normal range would be between .05% and 25%; and in 'steels when higher quality is required, phos- Carbon .48 Manganese 1.10 Silicon .25 Phosphorus .05 Sulphur .02 Selenium .09

In this steel a slight increase of phosphorus was deliberately provided because the selenium was considerably below the optimum percentage for easiest machining and yet the steel was found to have excellent machining propertiesparticularly when subjected to the difficult operation of gun barrel drilling. The anti-friction, nongalling property which is characteristic of steels containing sulphur, selenium or tellurium was also notable in this steel. The above example illustrates the maximum amount of non-ferrous alloy permissible under my definition of straight carbon steel, the alloys in this case adding up to 1.99%.

My invention as applied to mild steel for screw machine purposes is well embodied in the following example:

Carbon .15 Manganese .75 Silicon .12 Phosphorus .008 Sulphur .030 Selenium .10

Such steel machines as well, or slightly better, than'S. A. E. 1120 with which it was compared, and promises greater utility because of its relative cleanness and freedom from slag-like inclusions.

I have also made high carbon tool steels containing selenium and have found them to be free -.machining compared to similar steels without selenium, and without loss of their normal ability to harden and without apparent loss to their cut-' ting quality as tools. Such high carbon tool steels are well known to the art containing from about .90% to about 1.50% carbon and at least 98% iron. An example of such free machining high carbon tool steel is given in the following analysis:

Carbon 1.11 Manganese .29 Silicon .29 Phosphorus .013 Sulphur .011 Selenium .20

by the steel with less loss by volatilization. In themanufacture of low and medium carbon straightcarbon steels in an open hearth furnace, the selenium is best added in the ladle by introducing it into the flowing stream during tapping. The loss will depend upon the condition selenium alloy is heavy and is better assimilated of the metal and may range from 50% upwards,

particularly when a content of more than 15% selenium is sought. In the manufacture of high carbon tool steel in the induction electric furnace the iron selenium alloy can best be added to the bath a few minutes before tapping. The losses may range from 10% for a .10% selenium addition, up to for a .30% selenium addition. In the electric arc furnace the iron selenium alloy is best added at the time of tapping but the losses will be less than the open hearth additions because the condition of the metal is better.

I have tested the machinability of "straight carbon steels as described above both in the cast and rolled condition and find that my invention applies equally well to castings and rolled, forged or drawn products. 4

Having clearly set forth my invention I claim:

1. A substantially straight carbon steel containing more than 98% iron, .03% to 1.50% metalloid of the group selenium-tellurium, .05% to phosphorus and characterized by relatively free machining properties.

2. A substantially straight carbon steel as set forth containing more than 98% iron, .03% to 1.50% selenium and characterized by relatively free machining properties.

3. A substantially straight carbon steel as set forth containing more than 98% iron, .03% to 1.50% selenium, .05% to .50% phosphorus and characterized by relatively free machining properties.

4. A substantially straight carbon steel as set forth, containing more than 98% iron, between .05% and .40% of selenium and characterized by relatively free machining properties.

5. A substantially straight carbon steel as set forth, containing more than 98% iron, between .05% and .40% of selenium, .05% to 25% phos- 7 I phorus and characterized by relatively free machining properties. I

6. A ,straight carbon tool steel containing more than 98% iron, carbon between .90% and 1.50%, selenium .05% to 30% and characterized by relatively free machining properties.

' 7. A straight carbon tool steel containing more than 98% iron, carbon between .90% and 1.50% selenium .05% to 30%, .05% to .12% phosphorus and characterized by relatively free machining properties.

8. A relatively free machining iron containing 03% to 1.50% selenium, balance substantially all iron.

9. A relatively free machining iron containing .03% to 1.50% selenium, .05% to 50% phosphorus and balance substantially all iron.

FRANK R. PALIVIER. 

